Traditionally, vehicles have been provided with antennas mounted in different locations of the vehicle, being two of the most common locations the rear window (backlite) or roof location, for transmitting and receiving purposes. However, nowadays, these conventional antennas, specially the roof antennas that are typically designed as monopoles, do not achieve to provide an omni-directional coverage on all vehicles where are installed for all the frequencies and services considered in the vehicle environment. In the roof, depending on the frequency of operation (therefore the service) and the tilt of the roof, there are some directions that are not being covered, and therefore, the antenna is not acting with an omni-directional pattern. The tilt of the roof acts as an obstacle and makes that the antenna radiation is not omni-directional.
In these situations in which the shape of the roof acts as an obstacle, conventional antennas are unable to provide an adequate forward communication for the vehicle. As it can be seen in FIG. 1, the forward lobe of the antenna is mainly affected by the roof of the vehicle, since it acts as a reflector plane. Consequently, the forward lobe of the antenna radiation pattern is raised forming an α-degree angle with respect to a horizontal plane, parallel to the ground, and an antenna misalignment is induced.
Aesthetic and aerodynamic changing trends constitute the reasons why the antenna proper performance has been affected. Automotive industry has to satisfy customer tastes which generally lead vehicles to have a streamlined and smooth appearance, at the same time that favors the fulfillment of aerodynamic performance, another requirement in the automotive industry.
On the other hand, while antennas for receiving RF signals, such as those generated by AM/FM terrestrial broadcast stations have been a main focus of automotive industry, new bands for communication are being increasingly demanded by customers, consumer electronics trends, and even standardization bodies. Both wireless and satellite communications have been implemented by numerous applications and devices, so, currently, meeting customer demands for wireless and satellite communication applications in the vehicle, is mandatory for the automotive industry.
There is, in fact, a trend in using higher operating frequencies for new communication services. In the case of traditional antennas mounted on the roof of the vehicle, the forward radiation of the antenna (as shown in FIG. 1), is being more affected due to the tilt of the roof.
Therefore, it would be desirable to develop an improved antenna for a vehicle that is capable of providing a robust communication for both forward and backward directions and therefore acting with an omni-directional behavior, at the same time that is capable of transmitting and/or receiving RF signals in each of the different frequency bands demanded by the wireless and satellite communication applications.
Additionally, it is still desired a high-performing antenna that, when installed on a vehicle, does not alter the aesthetic appearance of the vehicle nor creates a substantial visual obstruction for the driver.